Formation of bone

ABSTRACT

Compositions and methods for inducing or promoting repair of a bone fracture.

FIELD OF THE INVENTION

The invention relates to formation of bone, including repair of bonewounds and fractures, and to elastin.

BACKGROUND OF THE INVENTION

Reference to any prior art in the specification is not an acknowledgmentor suggestion that this prior art forms part of the common generalknowledge in any jurisdiction or that this prior art could reasonably beexpected to be understood, regarded as relevant, and/or combined withother pieces of prior art by a skilled person in the art.

It is estimated that up to 2.2 million bone grafting procedures areperformed annually [1]. As a result of injury or tumour resection, theloss of large quantities of bone tissue can overwhelm the body's naturalbone healing capacity, leading to non-union. Together with infection,poor bone healing associated with major bone loss remain key challengesfor orthopaedic medicine.

Non-union results in recurrent surgical procedures and long in-hospitalstays which is challenging for both patients and surgeons [2, 3]. Two ofthe key causes that lead to non-union are an insufficiency of biologicalfactors required for repair, and infection of the bone (osteomyelitis)[3, 4].

Insufficient biological factors can result from a large bone defectsize, lack of biological growth factors (which can be further depletedby wound debridement) as well as damaged or reduced blood supply.Current treatments to restore osteogenic factors and an appropriatemicroenvironment include bone grafting [5], bone transport [6, 7],addition of growth factors and tissue engineering approaches.Nevertheless, all of these methods have limitations and there is anongoing search for more effective agents.

WO2012/068619, WO2014/063194 and WO2014/089610 discuss utilising thestructural characteristics of tropoelastin for formation of hydrogels,scaffolds and the like. These structures may then be adapted for use intherapeutic applications by attaching or seeding them with biologicalfactors or cells that are required for therapy at a site or locationwhere the structure is to be placed. Where therapy requires boneformation, WO2012/068619, WO2014/063194 and WO2014/089610 disclose thatit is the biological factors (for example bone morphogenic proteins) orcells (osteocytes) attached to the tropoelastin-based structure thatprovide for the therapy.

There is a need for new approaches to bone formation in therapeuticapplications.

SUMMARY OF THE INVENTION

The invention seeks to address one or more of the above mentioned needsor limitations, or to provide an alternative approach to bone formationand in one embodiment provides a use of tropoelastin or compositionsincluding same for inducing or promoting bone formation.

In another embodiment there is provided tropoelastin or compositionsincluding same for use in inducing or promoting bone formation.

In another embodiment there is provided tropoelastin or compositionsincluding same in the manufacture of a medicament for use in inducing orpromoting bone formation. The medicament may take the form of acomposition, formulation, scaffold, matrix or hydrogel, as describedbelow.

In another embodiment there is provided a method for inducing orpromoting bone formation including:

-   -   providing an individual requiring bone formation,    -   providing an amount of tropoelastin effective for inducing or        promoting bone formation to the individual,

thereby inducing bone formation in the individual.

Typically the tropoelastin is provided to a site or region of bone orbone-related tissue in which bone formation is required.

In other embodiments there is provided a use of tropoelastin orcompositions including same for inducing anabolism of bone.

In another embodiment there is provided tropoelastin or compositionsincluding same for use in inducing anabolism of bone

In another embodiment there is provided tropoelastin or compositionsincluding same in the manufacture of a medicament for use in inducinganabolism of bone. The medicament may take the form of a composition,formulation, scaffold, matrix or hydrogel, as described below.

In another embodiment there is provided a method for inducing anabolismof bone including:

-   -   providing an individual requiring induction of bone anabolism,    -   providing an amount of tropoelastin effective for inducing        anabolism of bone to the individual,

thereby inducing anabolism of bone in the individual.

Typically the tropoelastin is provided to a site or region of bone orbone—related tissue in which anabolism of bone is required.

In other embodiments there is provided a use of tropoelastin orcompositions including same for increasing the volume or density of bonetissue.

In another embodiment there is provided tropoelastin or compositionsincluding same for use in increasing the volume or density of bonetissue.

In another embodiment there is provided tropoelastin or compositionsincluding same in the manufacture of a medicament for use in increasingthe volume or density of bone tissue. The medicament may take the formof a composition, formulation, scaffold, matrix or hydrogel, asdescribed below.

In another embodiment there is provided a method for increasing thevolume or density of bone tissue including:

-   -   providing an individual requiring increased bone tissue volume        or density,    -   providing an amount of tropoelastin effective for increasing the        volume or density of bone tissue to the individual,

thereby increasing the volume or density of bone tissue in theindividual.

Typically the tropoelastin is provided to a site or region of bone orbone—related tissue in which increased volume or density of bone tissueis required.

The above described methods or uses may be applied to strengthen bone,to repair a bone defect, or to other clinical outcome in which boneformation is necessary.

In the above described methods or uses, the tropoelastin may be providedto the individual or site or region of bone or bone—related tissue inthe form of a composition, formulation, scaffold, matrix or hydrogel, asdescribed below.

Further aspects of the present invention and further embodiments of theaspects described in the preceding paragraphs will become apparent fromthe following description, given by way of example and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 — Biomechanical behaviour of bone before and after injection oftropoelastin hydrogel

FIG. 2 — The subcutaneous injection site of the tropoelastin hydrogelsat different time points.

FIG. 3 — Haematoxylin and eosin (H & E) staining of implants after 1 and2 weeks following injection. The results of the staining showed areduction in inflammatory response after 1 week (indicated with anarrow). Milligan's trichome (MT) staining of samples at week 2demonstrates fibroblast infiltration and collagen deposition.

FIG. 4 — Osteotomy in ovine model of bone repair (A) and followingtreatment with injectable tropoelastin-containing gels (B and C). Blackarrows indicate the osteotomy site.

FIG. 5 — Ovine model of bone repair. A: the three different types oftissues detected: cortical bone, trabecular bone and bone marrow. B:Control, MT stained at 8 weeks. C: Test samples (treated withtropoelastin gel) MT stained at 8 weeks. D: Immature woven bone wasformed in the control samples and was denser at the periosteal-facingsurfaces as compared with the endosteum region. Bone marrow was presentat the endosteum region. E. Strong cortical bone was formed at theendosteum end in the tropoelastin gel-treated samples. The osteotomy gapwas decreased from 3 mm to 1.8 mm.

FIG. 6 —CT images of osteotomy sites in the ovine model of bone repair.Images taken at 0, 4 and 8 weeks post-surgery and show portion ofosteotomy with the largest gap remaining.

FIG. 7 —Rabbit model of critical sized bone defect repair. A=site ofinjury prior to treatment. B=site of injury following injection oftropoelastin gel at Day 0.

FIG. 8 —μCT results, rabbit model of bone defect repair. OCc=control;OCte=treated with tropoelastin. *=differs significantly between the twogroups.

FIG. 9 —sequence of the tropoelastin SHELδ26A isoform

DETAILED DESCRIPTION OF THE EMBODIMENTS

The inventors provide herein tropoelastin and compositions includingsame that are suitable for use in promoting or inducing bone productionor formation and that advantageously have properties of being adherentto bone, injectable, angiogenic, osteogenic and/or bioabsorbable.According to the invention, tropoelastin is utilised principally toinduce the formation or production of bone in clinical applicationswhere bone production or formation is required.

A. Definitions

The term “comprise” and variations of the term, such as “comprising”,“comprises” and “comprised”, are not intended to exclude furtheradditives, components, integers or steps.

“Bone” generally refers to a mineralized tissue primarily comprising acomposite of deposited calcium and phosphate in the form ofhydroxyapatite, collagen (primarily Type I collagen) and bone cells suchas osteoblasts, osteocytes and osteoclasts, as well as to bone marrowtissue. Bone is a vascularised tissue.

Bone is generally in the form of “compact bone” (or “cortical bone”) or“spongy bone” (or “cancellous bone”). From a gross anatomicalperspective there are clear differences between compact and spongy bone.Specifically, compact bone has a lamellar structure and generallyrepresents a dense area of bone tissue that does not contain cavities,whereas spongy bone contains numerous interconnecting cavities definedby complex trabeculae. Compact bone is typically harder, stronger andstiffer than cancellous bone. The higher surface area to mass ratio ofcancellous bone compared to compact bone means that cancellous bone isless dense than compact bone and is generally softer, weaker and moreflexible than compact bone. Cancellous bone is highly vascularised andis typically found at the ends of long bones, proximal to joints andwithin the interior of vertebrae. Compact bone typically forms a “shell”around cancellous bone and is the primary component of the long bones ofthe arm and leg and other bones, where its greater strength and rigidityare needed. The primary anatomical and functional unit of compact boneis the osteon and the primary anatomical unit of cancellous bone is thetrabecula.

“Long bones” are generally bones in which compact bone is found at thediaphysis, which is the cylindrical part of the bone, whereas the spongybone is found at the epiphyses, i.e. the bulbous ends of a bone.Examples of long bones include humerus, radius, ulnar, tibia, fibularand femur.

“Short bones” are generally bones where there is usually a core ofspongy bone completely surrounded by compact bone. Examples include thebones of the hand.

“Flat bones” generally have 2 layers of compact bone called platesseparated by a layer of spongy bone. Examples of flat bones includeparietal, frontal, occipital and temporal bones of the skull, themandible and maxilla.

“Endochondral ossification” generally refers to production of bonewithin cartilage tissue, as generally occurs in fetal skeletal systemdevelopment. This bone production generally occurs at a primaryossification centre at the diaphyses, and then at a secondaryossification centre at the epiphyses. Endochondral ossification isgenerally required for formation of long and short bones.

“Intramembranous ossification” is another important process fordevelopment of the fetal skeletal system, although unlike endochondralossification, intramembranous ossification generally refers toproduction of bone that does not occur within cartilage. Intramembranousossification is generally required for formation of flat bones.Intramembranous ossification is also an essential process during thenatural healing of bone fractures

“Subchondral bone” is generally bone located below cartilage, andtherefore generally provides support for a cartilaginous articularsurface.

“Bone-related tissue” generally refers to tissue that is eithersupported by bone (for example articular tissue) or tissue that isconnected to bone, for example, a ligament or tendon. Generally,bone-related tissue is cartilaginous.

“Inducing or promoting bone formation” generally refers to an anabolicprocess the end result of which is bone. Generally this does not involvea catabolic process that leads to re-modelling of bone. However, thebone arising from inducing or promoting bone formation in accordancewith the invention may be remodelled with or without clinicalintervention. In certain embodiments the induction or promotion of boneformation involves a process that more closely resembles intramembranousossification. As described herein and exemplified in the examples, theprocess generally involves the proliferation and differentiation ofosteoblasts and the mineralisation of calcium. The process may or maynot require the presence of cartilaginous tissue.

A “bone defect” is generally a structural disruption of bone requiringrepair. A defect can assume the configuration of a “void”, which isunderstood to mean a three-dimensional defect such as, for example, agap, cavity, hole or other substantial disruption in the structuralintegrity of a bone or joint. A defect can be the result of accident,disease, surgical manipulation, and/or prosthetic failure. The defectmay be a void having a volume incapable of endogenous or spontaneousrepair. Generally, these are capable of some spontaneous repair, albeitbiomechanically inferior. Other defects susceptible to repair include,but are not limited to, non-union fractures; bone cavities; tumorresection; fresh fractures (distracted or undistracted); cranial/facialabnormalities; periodontal defects and irregularities; spinal fusions;as well as those defects resulting from diseases such as cancer,arthritis, including osteoarthritis, and other bone degenerativedisorders such as osteochondritis dessicans.

“Repair” generally refers to new bone formation which is sufficient toat least partially fill a void or structural discontinuity at a defect.Repair does not, however, mean, or otherwise necessitate, a process ofcomplete healing or a treatment which is 100% effective at restoring adefect to its pre-defect physiological/structural/mechanical state.

When a bone is fractured, the damaged blood vessels produce a localizedhaemorrhage with formation of a blood clot. Destruction of bone matrixand death of bone cells adjoining the fracture may also occur. Duringrepair, the blood clot, the remaining cells, and the damaged bone matrixmay be removed by macrophages. The periosteum (the connective tissuemembrane covering the bone) and the endosteum (the thin vascularmembrane of connective tissue that lines the surface of the bony tissuethat forms the medullary cavity of long bones) around the fracturerespond with intense proliferation of osteoprogenitor cells, which forma cellular tissue surrounding the fracture and penetrating between theextremities of the fractured bone. Immature bone is then formed byendochondral ossification of small cartilage fragments that appear inthe connective tissue of the fracture. Depending on the nature of thebone injury or fracture, the periosteum may be largely intact followingthe injury (i.e., still connected to the bone). In this scenario, theendosteum may or may not be damaged as a result of the injury andtherefore may or may not contribute to repair. In other circumstances,there may be significant destruction to the periosteum (for example, asignificant trauma or a surgical procedure), wherein the periosteum isno longer in contact with the bone surface. Under these circumstances,the contribution of the periosteum to bone repair may not be possiblewithout alternative intervention.

Bone is also formed by means of intramembranous ossification. Repairprogresses in such a way that irregularly formed trabeculae of immaturebone temporarily unite the extremities of the fractured bone forming a“bone callus”. Normal stress imposed on the bone during repair andduring return to activity serves to remodel the bone callus, influencingits structure, and the primary bone tissue of the callus is thereforegradually reabsorbed and replaced by lamellar bone, resulting inrestoration of the original bone structure and function.

“Tropoelastin” is generally a monomeric protein from which elastin isformed. Tropoelastin is generally not cross linked, covalently orotherwise. Tropoelastin may reversibly coacervate. Tropoelastin may besynthetic, for example it may be derived from recombinant expression orother synthesis, or it may be obtained from a natural source such asporcine aorta. As generally known in the art, tropoelastin may exist inthe form of a variety of fragments.

B. Bone formation

It will be understood that the invention applies to the induction orpromotion of bone formation. In one embodiment, there is provided amethod for inducing or promoting bone formation. The method includes thefollowing steps:

-   -   providing an individual requiring bone formation,    -   providing tropoelastin to the individual to induce or promote        the formation of bone in the individual,

thereby inducing bone formation in the individual.

The individual may require bone formation for the purpose of remedyingor repairing a bone defect. The bone defect may be a fracture, such as anon-union fracture or a fresh fracture (distracted or undistracted). Thebone defect may result in minor damage to the periosteum. In thiscircumstance, there may be no damage to the endosteum. Alternatively,the bone defect may include damage to both the periosteum and endosteum.The bone defect may be a fracture or microfracture made during acontrolled surgical procedure or as a result of a trauma. Thus in oneembodiment there is provided a method for repairing a bone fractureincluding the following steps:

-   -   providing an individual requiring repair of bone fracture,    -   providing tropoelastin to the individual to repair the bone        fracture in the individual,

thereby repairing a bone fracture in the individual.

In another embodiment the individual requires bone formation for thefilling of a void in bone tissue. The void may generally be a threedimension defect such as a gap, cavity or hole arising from disease,surgical manipulation and/or prosthetic failure. The void may have avolume incapable of endogenous or spontaneous repair. For example thevoid may be twice the diameter of the subject bone. Thus in anotherembodiment there is provided a method for filling a void in boneincluding the following steps:

-   -   providing an individual having a void in a bone,    -   providing tropoelastin to the individual to fill the void in the        bone of the individual,

thereby filling the void in the bone.

Typically the tropoelastin is provided to a site or region of bone orbone—related tissue in which bone formation is required. In thisembodiment, the tropoelastin is provided by local administration oftropoelastin to the site or region of bone or bone related tissue. Localadministration generally requires direct contact of the site or regionof bone or bone—related tissue with the tropoelastin.

The tropoelastin may be provided for direct contact with a site orregion of bone or bone—related tissue by applying tropoelastin in theform of a composition, formulation, scaffold or matrix described belowto the site or region of bone or bone related tissue. In more detail,and as described further herein, in some embodiments at least sometropoelastin contained in the formulation is not cross linked, bonded orotherwise covalently attached to other components of the composition orformulation, for example, not attached to a scaffold or matrix. Thisenables at least some, if not all tropoelastin provided in theseformulations to be released from the composition to tissue at the siteof bone or bone related tissue that requires repair, thereby enablingthe tropoelastin to stimulate the tissue elements at that site for boneproduction. The direct contact of the tropoelastin of these formulationswith the site of bone or bone-related tissue requiring bone formation orproduction enables tropoelastin to induce the formation or production ofbone at the site.

The tropoelastin may be applied to bone only, or to bone andbone-related tissue. For example, in the context of a surgical procedurethe tropoelastin may be applied to the bone only. Examples, of surgicalprocedures in which tropoelastin may be subsequently utilised to promotean osteoinductive or osteoconductive environment include: cranial, jawand dental repair, knee arthroscopy and meniscectomy; shoulderarthroscopy and decompression; carpal tunnel release; knee arthroscopyand chondroplasty; knee arthroscopy and anterior cruciate ligamentreconstruction; total knee replacement; repair of femoral neck fracture;repair of trochanteric fracture; knee arthroscopy repair of bothmenisci; total hip replacement; shoulder arthroscopy/distal clavicleexcision; repair of rotator cuff tendon; repair fracture of radius(bone)/ulna; laminectomy; repair of ankle fracture (bimalleolar type);shoulder arthroscopy and debridement; lumbar spinal fusion; repairfracture of the distal part of radius; lower back intervertebral discsurgery; incise finger tendon sheath; repair of ankle fracture (fibula);repair of femoral shaft fracture; repair of trochanteric fracture. Otherexamples of surgical procedures which may require the subsequentinduction of bone repair include cardiothoracic surgeries, which requirecutting of the sternum (a median sternotomy) to gain access to thethoracic contents.

The tropoelastin may be applied to periosteum only, or endosteum only,or to both periosteum and endosteum. For example, where bonemicrofracture or microdrilling has occurred, the tropoelastin willtypically be applied to the periosteum only. Where a full fracture ofthe bone has occurred through trauma (such as a bilateral fracture ofthe diaphysis of a long bone), the tropoelastin will typically beapplied to both the periosteum and the endosteum.

The tropoelastin may be applied to compact bone only, or spongy boneonly, or to both spongy and compact bone. For example, in the context ofa surface fracture of the bone, in which only the compact bone isdamaged, the tropoelastin will be applied to the compact bone only.Where both compact and spongy bone are damaged and an osteoinductive andosteoconductive environment is required, the tropoelastin may be appliedto both the spongy and compact bone. In microdrilling applications intoan articular surface supported by spongy bone, the tropoelastin may beapplied to spongy bone only.

Where the objective is to repair a defect in the form of a fracture, thetropoelastin may be applied by direct contact to the bone at the site ofthe fracture, including to one or more of the periosteum, endosteum, orcallus. In this embodiment the tropoelastin may be provided on or belowthe periosteum.

Where the objective is to fill a void in bone, for example a gap,cavity, hole or other, the tropoelastin may be provided on or below theperiosteum.

In one embodiment, the method is for formation of intramembranous bone,or formation of spongy bone, or both.

As described herein, the invention further provides for inducing theanabolism of bone. Specifically, as exemplified herein, the inventorshave found improvements in bone formation seen with tropoelastintreatment result from a mechanism primarily involving bone anabolism.The finding is significant as few other biological factors have beenfound to have this function. Bone anabolism is particularly requiredwhere there is a clinical need to increase bone density, or to increasebone volume. Thus in one embodiment there is provided a method forinducing anabolism of bone including:

-   -   providing an individual requiring induction of bone anabolism,    -   providing an amount of tropoelastin effective for inducing        anabolism of bone to the individual,

thereby inducing anabolism of bone in the individual.

In one embodiment, the individual may require treatment to increase bonedensity. For example, the individual may have a form of osteoporosis.

In another embodiment, the invention provides for increase in volume ofbone tissue. In this embodiment, the outcome of anabolism may beincreases in any one or more dimensions of bone. This treatment may beparticularly relevant where the intention is to improve the volume of animproperly formed bone. Thus there is provided a method for increasingthe volume of bone tissue including:

-   -   providing an individual requiring increased bone tissue volume,    -   providing an amount of tropoelastin effective for increasing the        volume of bone tissue to the individual,

thereby increasing the volume of bone tissue in the individual.

Where the objective is to repair a defect in the form of low bonedensity (such as due to osteoporosis), the tropoelastin may be appliedby direct contact to the bone including to one or more of theperiosteum, endosteum, or callus. In this embodiment the tropoelastinmay be provided on or below the periosteum. In a further embodiment, thetropoelastin may be provided to an endosteum region by micro-drilling ofcortical bone.

In the above described embodiments tropoelastin may be applied tosubchondral bone, i.e. adjacent bone related tissue, or it may becontacted with bone to permit bone formation in the absence ofcartilaginous tissue.

The tropoelastin may be applied to a long bone, short bone or flat bone.

In one embodiment, the method may involve the administration of afurther compound for influencing bone production. The compound may beone that is anabolic, in the sense that it is involved in new boneproduction, or catabolic, in the sense of causing bone re-sorption.

For the treatment of fracture, a composition containing from 0.1 mg/mlto 100 mg/ml of tropoelastin, preferably from 1.0 to 75 mg/mltropoelastin, more preferably from 2.0 to 50 mg/ml tropoelastin may beprepared in sterile water. The composition is preferably prepared as aninjectable composition.

The composition is generally injected into the site of the injury. Inone embodiment it is preferable to inject directly into the soft tissueadjacent to the fracture. In another embodiment it could be administeredby intra osseous injection. This could be performed in saline,injectable ceramic, or other high viscosity carrier.

Preferably the injection permits tropoelastin to be delivered to atleast one, and more preferably, one or more opposing surfaces formedfrom the fracture. Generally it is preferable to achieve an evenapplication of the tropoelastin across all of the relevant opposingsurfaces.

Clinically the preferred method would be to apply via surgical meansonly a single time with or without other agents. Follow up doses bypercutaneous injection or topical application could be applied. Followup dosing could be a preferred method for preventing or treating boneinfection. Alternatively an implant could be used that allows forsustained in vivo dosing using tropoelastin. One example of this couldbe the use of sucrose acetate isobutyrate.

Injections, including follow up injections, may be made more than once aweek, and typically twice a week i.e. ‘biweekly’. The injections may beadministered for a period of about three to four weeks.

In one embodiment, a bolus of tropoelastin may be delivered by injectionof tropoelastin more or less immediately after fracture

In another embodiment, the tropoelastin may be applied in the form of ahydrogel, putty, paste, sponge or scaffold. Acellular collagen spongesor other bioresorbable carriers may be preferred. This could include acarboxymethylcelulose, a collagen putty or a high viscosity carriermedium such as sucrose acetate isobuyrate. It could also be deliveredvia polymer scaffolds, including PLLA, PLGA, PGA, PCL. It could also beapplied topically or by direct injection.

In one embodiment, tropoelastin could be applied into the fracture atthe time of fracture or prior to casting for closed fractures. For openfractures it could be introduced to the fracture gap after debridementof the wound area. For wounds where infection is suspected it could beinjected adjacent to the healing fracture or into the intra osseousspace as mentioned above.

The outcome of the treatment may be observed by reference to CD31 andTRAP staining of the fracture site. Generally the expression of thesemolecules is expected. Further a callus may be formed, although softtissue is unlikely to have formed by the 3 week end point. Preferablythe treatment should lead to normal progression of endochondral bonehealing. This involves a cartilaginous soft callus being progressivelyreplaced by woven bone, which is then remodelled into lamellar/corticalbone.

The effective amount of the tropoelastin may be expected to varydepending upon the circumstances in which bone formation is required. Itwould be well within the skill of persons skilled in the art to adjustthe amount appropriately to obtain optimal results. It is, however,expected that generally the effective amount of the agent will be in therange of 0.1 to 100,000 μg per kg of body weight, more preferablybetween 1 and 10,000 μg per kg of body weight, and most preferablybetween about 10 and 1,000 μg.

In certain embodiments the tropoelastin may be provided in doses of fromabout 0.5 mg to 2000 mg, preferably from 0.5 to 100 mg, more preferablyfrom 1 to 50 mg.

C. Formulations

C.1 Tropoelastin, the Active Agent for Inducing Bone Formation

The tropoelastin utilised in the present invention for stimulating orinducing or promoting bone formation or production may be obtained bypurification from a suitable source (eg from humans or other animals) orproduced by standard recombinant DNA techniques such as is described in,for example, Maniatis, T. et al., [8].

Recombinant tropoelastin may incorporate modifications (eg amino acidsubstitutions, deletions, and additions of heterologous amino acidsequences), thereby forming tropoelastin analogues which may, forexample, enhance biological activity or expression of the respectiveprotein.

In a preferred embodiment, the methods of the invention utilise theSHELδ26A analogue (WO 1999/03886) [9] for the various applicationsdescribed herein including for inducing or promoting bone growth, forincreasing anabolism of bone, for increasing bone density or volume, orfor fracture repair, or correcting a defect or void in bone tissue. Theamino acid sequence of SHELδ26A is shown in SEQ ID No: 1 (see also FIG.9 ). In alternative embodiments, the tropoelastin isoform is the SHELisoform (WO 1994/14958) or a protease resistant derivative of the SHELor SHELδ26A isoforms (WO 2000/0403).

Tropoelastin analogues generally have a sequence that is homologous tohuman tropoelastin sequence. Percentage identity between a pair ofsequences may be calculated by the algorithm implemented in the BESTFITcomputer program [10].

Another algorithm that calculates sequence divergence has been adaptedfor rapid database searching and implemented in the BLAST computerprogram [11]. In comparison to the human sequence, the tropoelastinpolypeptide sequence may be only about 60% identical at the amino acidlevel, 70% or more identical, 80% or more identical, 90% or moreidentical, 95% or more identical, 97% or more identical, or greater than99% identical.

Conservative amino acid substitutions (e.g., Glu/Asp, Val/Ile, Ser/Thr,Arg/Lys, Gln/Asn) may also be considered when making comparisons becausethe chemical similarity of these pairs of amino acid residues areexpected to result in functional equivalency in many cases. Amino acidsubstitutions that are expected to conserve the biological function ofthe polypeptide would conserve chemical attributes of the substitutedamino acid residues such as hydrophobicity, hydrophilicity, side-chaincharge, or size.

The codons used may also be adapted for translation in a heterologoushost by adopting the codon preferences of the host. This wouldaccommodate the translational machinery of the heterologous host withouta substantial change in chemical structure of the polypeptide.

Recombinant forms of tropoelastin can be produced as shown in WO1999/03886.

C.2 Formulations Comprising Tropoelastin

It will be understood that the tropoelastin is provided in theformulations of the invention for the purpose of exploiting thebiological activity of tropoelastin in inducing bone formation. In thiscontext, tropoelastin is an active ingredient of atropoleastin—containing composition for the induction of bone formation.

In a particularly preferred embodiment, the only active ingredient oragent for inducing bone repair in a formulation or composition of theinvention is tropoelastin. In this embodiment, the formulation does notcontain cells such as osteocytes or factors such as BMPs for inducingbone formation.

As discussed above, in some embodiments at least some tropoelastincontained in a formulation according to the invention is not crosslinked, bonded or otherwise covalently attached to other components ofthe composition or formulation, for example, not attached to a scaffoldor matrix. This enables at least some, if not all tropoelastin providedin these formulations to be released from the composition to tissue atthe site of bone or bone related tissue that requires repair, therebyenabling the tropoelastin to stimulate the tissue elements at that sitefor bone production.

Preferably, at least some of the tropoelastin provided in theformulation is substantially monomeric (i.e., is not intra-molecularlycross-linked to any significant extent with other components of theformulation) such that the tropoelastin that is provided to the site ofinjury is also monomeric and may be released from the formulation to thesite requiring bone production or formation.

In one embodiment, the tropoelastin provided in the formulation consistsof monomers that are not covalently cross-linked.

In yet a further embodiment, the tropoelastin in the formulation maycomprise both cross-linked and non-cross-linked forms of the protein,but will typically contain more non-cross-linked forms of the protein.

In one embodiment, no more than about 50% of the tropoelastin containedin the formulation is cross-linked with a biomolecule and/or biopolymer,such as a saccharide-containing molecule, for example, anoligosaccharide, polysaccharide, or derivatives thereof. In otherembodiments, no more than about about 40%, 30%, 20%, 10%, or 5% of thetropoelastin is cross-linked.

In certain embodiments, the number of tropoelastin molecules notincorporated into a cross-linked protein matrix or complex and leftunbound is preferably at least 50%, 60%, 70%, 80%, 90% or 95%.

In certain embodiments, the tropoelastin has a specified degree ofpurity with respect to the amount of tropoelastin in a composition foradministration, as compared with amounts of other proteins or moleculesin the composition. In one embodiment, the tropoelastin is in acomposition that has at least 75% purity, preferably 85% purity, morepreferably more than 90% or 95% purity. Fragments of tropoelastin, i.e.,truncated forms of a tropoelastin isoform that arise unintentionallythrough tropoelastin manufacture may be regarded as an impurity in thiscontext.

It will further be understood that in certain embodiments thetropoelastin may be provided in the form of a composition that consistsof or consists essentially of tropoelastin, preferably a full lengthisoform of tropoelastin. In alternative embodiments, the tropoelastinwill be at least 65% of the length of the relevant tropoelastin isoform,more than 80% of the full length, more than 90% or more than 95% of thefull length.

Typically, the tropoelastin formulations for use in accordance with thepresent invention have a tropoelastin concentration greater than about1.5 mg/mL (although lower concentrations may also be used). For example,a tropoelastin formulation having a concentration of tropoelastin fromabout 1.5 mg/mL to about 400 mg/mL is preferable. More preferably, theformulation will have a tropoelastin concentration between about 5 mg/mLto about 300 mg/mL yet more preferably about 10 mg/mL to about 200 mg/mL.

Typically a formulation of the invention contains a component definingthe mechanical, or physical properties of the formulation. Examples ofthese properties, in the context of hydrogels as examples offormulations of the invention are described below. Further described areexamples of components which are generally water binding, long chain orpolymeric molecules including hyaluronic acid.

C.3 Hydrogels Typically, a hydrogel for use according to the inventioncomprises:

-   -   polymeric hydrophilic molecules forming a scaffold and imbuing        the hydrogel with mechanical properties described below;    -   water; and    -   tropoelastin for inducing or promoting bone production or        formation.

As described below, examples of polymeric hydrophilic molecules includecarboxymethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, hyaluronic acid, xanthan gum, guar gum, β-glucan,alginates, carboxymethyl dextran.

In one embodiment, a hydrogel according to the invention may provide fora tensile strength of from 100 kPa to 2 MPa. Tensile strength is usuallydefined as the maximum stress that a material can withstand while beingstretched or pulled before the material's cross-section starts tosignificantly stretch. A person skilled in the art will be aware ofsuitable methods to test the ultimate strength of a material. Thehydrogel of the present invention can have an ultimate strength rangingfrom about 10 to about 45 kPa (for example, about 12 to about 40 kPa).

In another embodiment the hydrogel has a compression strength of from 50kPa to 700 kPa. Compressive strength is the capacity of a material orstructure to withstand axially directed pushing forces. It provides data(or a plot) of force vs deformation for the conditions of the testmethod. By definition, the compressive strength of a material is thatvalue of uni-axial compressive stress reached when the material failscompletely. The compressive strength is usually obtained experimentallyby means of a compressive test. The apparatus used for this experimentis the same as that used in a tensile test. However, rather thanapplying a uni-axial tensile load, a uni-axial compressive load isapplied. As can be imagined, the specimen is shortened as well as spreadlaterally. Compressive strength is often measured on a universal testingmachine; these range from very small table-top systems to ones with over53 MN capacity. Measurements of compressive strength are affected by thespecific test method and conditions of measurement.

Compressive strength of the hydrogels can be determined using cyclicloading at a given strain level (for example, 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75% strain level). Thecompressive modulus of the hydrogels can range from about 1 kPa to about500 kPa.

Under compression, the hydrogels can lose energy. Energy loss can rangefrom about 5% to about 50%. In some embodiments, energy loss can be fromabout 10% to about 40%, from about 20% to about 35% (for example,23±3.2% or 24.1±7%), or from about 25% to about 30% (for example,30.5±6.4 or 26.9±2.3).

In one embodiment, the strain at break of the hydrogel between about 130and about 420 kPa. The strain at break test is performed by stretchingsamples until they break and determining the strain at breaking pointfrom the strain/stress curves.

In certain embodiments, the tropoelastin formulations for use inaccordance with the present invention, may have an elastic modulus ofbetween about 500 Pa to about 50 Pa, about 450 Pa to about 100 Pa, about400 Pa to about 125 Pa; about 400 Pa to about 150 Pa, or about 385 Pa toabout 150 Pa. The elastic modulus will vary depending on theconcentration and components used.

In certain embodiments, the hydrogels may have an extrudable length,that is substantially coherent and substantially holds together withoutsupport, of at least about 5 cm, 10 cm, 12 cm, 15 cm, 18 cm, 20 cm, or25 cm when extruded through a 25G needle. Certain embodiments may havean extrudable length, that is substantially coherent and substantiallyholds together without support, of at least about 5 cm, 10 cm, 12 cm, 15cm, 18 cm, 20 cm, or 25 cm when extruded through a 27G needle. Certainembodiments may have an extrudable length, that is substantiallycoherent and substantially holds together without support, of at leastabout 5 cm, 10 cm, 12 cm, 15 cm, 18 cm, 20 cm, or 25 cm when extrudedthrough a 30G needle or 31G needle.

Certain embodiments may have an extrudable length of at least about 5cm, 10 cm, 12 cm, 15 cm, 18 cm, 20 cm, or 25 cm through a fine gaugeneedle.

The hydrogels for use in accordance with the present invention may alsobe swellable. The term “swellable” refers to hydrogels that aresubstantially insoluble in a swelling agent and are capable of absorbinga substantial amount of the swelling agent, thereby increasing in volumewhen contacted with the swelling agent. As used herein, the term“swelling agent” refers to those compounds or substances which produceat least a degree of swelling. Typically, a swelling agent is an aqueoussolution or organic solvent, however the swelling agent can also be agas. In some embodiments, a swelling agent is water or a physiologicalsolution, for example phosphate buffer saline, or growth media.

In some embodiments, the hydrogel comprises a swelling agent. In someembodiments, the hydrogel can contain over 50% (w/v), over 60% (w/v),over 70% (w/v), over 80% v, over 90% (w/v), over 91% (w/v), over 92%(w/v), over 93% (w/v), over 94% (w/v), over 95% (w/v), over 96% (w/v),over 97% v, over 98% (w/v), over 99% (w/v), or more of the swellingagent.

The term “swelling ratio” is used herein to mean weight of swellingagent in swollen hydrogel per the dried weight of the hydrogel beforeswelling. For example, the swelling ratio can range from about 1 toabout 10 grams of swelling agent per gram of the tropoelastin in thehydrogel. In some embodiments, the swelling ratio can be from about 1 toabout 5 grams of swelling agent per gram of the tropoelastin in thehydrogel. In some embodiments, the swelling ratio can be about 1.25,about 1.5, about 1.75, about 2, about 2.25, about 2.5, about 2.75, about3, about 3.25, about 3.5, about 3.75, about 4, about 4.25, about 4.5,about 4.75 or about 5 grams of swelling agent per gram of tropoelastinin the hydrogel. In some embodiments, the swelling ratio can be 1.2±0.2,2.3±0.3, or 4.1±0.3 grams of swelling agent per gram of tropoelastin inthe hydrogel.

In a preferred embodiment, the tropoelastin formulations used inaccordance with the present invention, are hydrogels which have suitablepersistence properties such that the formulation is maintained at thesite of delivery for a sufficient period to enable release oftropoelastin at multiple times so that tropoelastin can exert itsbiological effect. In other words, the hydrogel will typically have a‘residence time’ at the site of delivery of more than 1 week, preferablyat least 2 weeks.

In certain embodiments, a hydrogel generally has a functionality (i.e.water-binding, mechanical strength, phase-transition and cross-linking)suitable for application as a bone filler for inducing or promoting bonewound repair. According to the invention, this functionality principallyarises from components other than tropoelastin. These components may bepolymeric and are described in more detail below. The tropoelastin isprovided in the hydrogel for the purposes of promoting bone formation.

The skilled person will appreciate that hydrogels can be used asscaffolds for tissue engineering applications because of theirbiocompatibility and high water content, which resemble the naturaltissue microenvironment. Further, the skilled person will appreciatethat various methods exist for modifying the mechanical properties ofthe hydrogels, including the extensibility of the hydrogels tofacilitate increased residence time at the site of delivery, and therebyproviding for an increased release time for the active agent (in thiscase, according to the invention, tropoelastin) contained within thehydrogel.

In one embodiment, after formation of the hydrogel, the hydrogel may bedried to provide a polymeric substrate including the tropoelastin. Inthis embodiment, the polymeric substrate is the component for providingstructure and function referred to above. This dehydrated compositionmay then be sold for use in bone repair and re-hydrated in sterileconditions before clinical use.

The hydrogels utilised in the invention have properties of flow thatenable injection to the site of bone defect or wound. This is adistinguishing feature over other elastomeric bone fillers. Further toinjection capability, this enables the hydrogel to flow across thesurface of the relevant bone site, providing extensive and completecontact with the bone surface, thereby improving or accelerating bonerepair.

In one embodiment, the phase transition characteristics of thecomponents that form the hydrogel may enable the hydrogel to set at bodytemperature, thereby ostensibly forming a substrate or graft that is inextensive contact with bone tissue across the wound site. The hydrogelsfor use in accordance with the present invention are distinguished fromother elastomeric bone fillers which are placed at the wound site as asolid pre-fabricated structure that therefore has limited and notextensive contact with the bone surface across the wound site.

In certain embodiments, the formulations of the invention herein mayhave properties of flow at 20 to 37° C., preferably less than 45° C.enabling delivery of the formulation to the site by injection.

Typically a hydrogel utilised in the invention for bone wound repair isone having properties of flow enabling injection of the hydrogel througha needle with a gauge of between 18G and 32G, preferably 26G to 31G,more preferably 27G with minimal thumb backpressure. This injectionpressure is less than 350 kPa which is well below the acceptablepressure range for disposable syringes.

In certain preferred embodiments, the hydrogels of the present inventioninclude Hyaluronic acid (HA) for use as a scaffold. In thesecircumstances, the HA functions to provide certain mechanical propertiesto the hydrogel, allowing the tropoelastin to remain substantially free(un-crosslinked), such that the tropoelastin has the ability to functionas a biological factor, stimulating and inducing bone formation at thesite where the hydrogel is provided.

In certain embodiments, where the hydrogel includes tropoelastin andhyaluronic acid, the mass ratio of tropoelastin to hyaluronic acid is0.1:1 to about 500:1, preferably, about 0.2:1 to about 100:1.

In yet further embodiments, the hydrogel may comprise HA in aconcentration of between about 0.1% to about 15%. In certainembodiments, the hydrogel may comprise the HA in a concentration ofbetween about 0.1% to about 10%.

The hydrogel may comprise derivatised HA or underivatised HA, to controlthe extent to which the HA crosslinks with itself and/or the monomericprotein.

In certain embodiments, the HA may comprise, at least one linkablemoiety, such as at least one cross-linkable moiety, for example, acarboxyl group, a hydroxyl group, an amine, a thiol, an alcohol, analkene, an alkyne, a cyano group, or an azide, and/or modifications,derivatives, or combinations thereof.

In certain embodiments, the HA may comprise, a spacer group, such thatthe spacer group is capable of linking to the same and/or a secondmolecule, for example, a second biomolecule or biopolymer.

The HA used in the hydrogel may be in the range of about 100 to 300saccharide units or residues, for example around 200 saccharide units orresidues. In other embodiments, hyaluronic acid may be used in the rangeof 200 to 20,000 saccharide units or residues.

In certain embodiments, the HA may be low or high molecular weight, andthe choice of which will vary depending on the skilled person'sintentions for modifying the viscosity of the hydrogel. For example, useof lower molecular weight hyaluronic acid allows the hyaluronic acid tobe modified, precipitated and washed and the hyaluronic acid remains areasonably low viscous solution that may be readily used as thecross-linking agent. Using higher molecular weight polysaccharides mayprovide additional handling issues (e.g., viscous solution, problemswith mixing, aeration etc) but, in certain embodiments, a wide range ofmolecular weights may be used to achieve the desired results.

In certain embodiments, the HA may be activated and/or modified with anactivating agent, such as EDC or allylglycidyl ether, and/or modifyingagent, such as NHS, HOBt or Bromine.

The term “hyaluronic acid” or “HA” may include hyaluronic acid and anyof its hyaluronate salts, including, for example, sodium hyaluronate(the sodium salt), potassium hyaluronate, magnesium hyaluronate, andcalcium hyaluronate. Hyaluronic acid from a variety of sources may beused herein. For example, hyaluronic acid may be extracted from animaltissues, harvested as a product of bacterial fermentation, or producedin commercial quantities by bioprocess technology.

In one embodiment, the hydrogels of the present invention include thepolymer poly(NIPAAm-co-NAS-co-(HEMA-PLA)-co-OEGMA) (PNPHO; preferably apolymer having 73% N-isopropyl acrylamide, 8% lactide, 5% ethyleneglycol, 14% N-acryloxysuccinimide formulation).

In the PNPHO-tropoelastin hydrogels, the tropoelastin and PNPHO havedefined roles. The tropoelastin serves as the source of bioactivesignalling for bone regeneration, and the PNPHO acts as a scaffold toprovide properties of persistence to the hydrogel.

The PNPHO polymer is chemically bonded with tropoelastin to (a) adjustthe physicochemical properties of this biopolymer for bone applications,(b) to impart rapid thermosetting to the hydrogel filler to confine itlocally, and (c) to impart bioresorption properties to the injectablehydrogels. The combination of these two main segments results in theformation of the new class of smart bone fillers with a range offavourable properties for bone healing.

The skilled person will appreciate that in modifying the relativeproportions of tropoelastin to PNPHO, it is possible to modify theextent to which hydrogel provides tropoelastin in substantially freeform. In other words, by decreasing the proportion of PNPHO (andincreasing the overall proportion of tropoelastin) in the hydrogel, itis possible to increase the amount of free tropoelastin in the hydrogel,which is desirable for the present invention, since the tropoelastinneeds to be able to diffuse from the hydrogel to exert is physiologicaland biological effect.

In one embodiment, the final molar ratio of tropoelastin to PNPHO in thehydrogel is 10 (tropoelastin): 1 (PNPHO) In a preferred embodiment, thefinal molar ratio of tropoelastin to PNPHO in the hydrogel is 5:1, 4:1,3:1, 2:1, more preferably 1:1.

Suitable polysaccharides which may also be included in the hydrogelsinclude carboxy cellulose, carboxymethyl cellulose, hydroxymethylcellulose, hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose(HPMC), hydroxy-propylcellulosecarboxymethyl amylose (“CMA”), xanthangum, guar gum, β-glucan, alginates, carboxymethyl dextran, aglycosaminoglycan derivative, chondroitin-6-sulfate, dermatin sulfate,polylactic acid (PLA), or biomaterials such as polyglycolic acid (PGA),poly(lactic-co-glycolic) acid (PLGA), tricalcium phosphate (TCP),1-hydroxyapatite (PAH), and their pharmaceutically acceptable salts.Alternatively, the polysaccharide may be a pectin or a derivativethereof, including linear and branched polysaccharides.

When the scaffold agents used in the tropoelastin hydrogels iscarboxymethylcellulose or xanthan gum, the agent may be provided in anamount of from about 0.01 to 10 percent (w/v), preferably in an amountof from 0.5 to 3.5 percent (w/v).

The scaffold may be a cross-linked or uncross-linked polysaccharidetypically having a substitution or additional side chain.

Additional scaffold may include scaffolds derived frompolymethacrylates, polyethylene glycols and (block) copolymers withpolyethylene glycol subunits (for example Poloxamer 188 and Poloxamer407). Alternative agents included in the hydrogels include surfactantssuch as sodium lauryl sulfate and polysorbates, or pantothenol,polyethylene glycols, xanthan gum, guar gum, polysorbate 80,N-acetylglucosamine and their pharmaceutically acceptable salts.

Further aspects of the present invention and further embodiments of theaspects described in the preceding paragraphs will become apparent fromthe following description, given by way of example and with reference tothe accompanying drawings.

EXAMPLES Example 1 Biomechanical Properties of Tropoelastin Gel

An ex vivo, clean sharp tibia fracture model was used to assess thebiomechanical properties of tropoelastin provided in apoly(NIPAAm-co-NAS-co-(HEMA-PLA)-co-OEGMA) (PNPHO) hydrogel (TE-PNPHOhydrogel). Briefly, a TE-PNPHO hydrogel was injected into clean, freshcadaver sheep tibia fracture. The tropoelastin hydrogel adhered to thebone and filled the fracture, making contact with the fracture surfacesat and between the periosteal and endosteal margins, as shown in FIG. 1.

The test was repeated for 6 independent tibia fractures, and themechanical strengths of the bones were measured in each case.Surprisingly, 80% of the strength of the bone was recovered followinginjection of the tropoelastin hydrogel. This performance was modelled onthe injectable's tissue-adhesiveness properties, combined with theviscoelastic performance of the hydrogels. Control measurements werealso performed and confirmed that this effect was due to the presence oftropoelastin, since the mechanical performance was not restored in theabsence of tropoelastin.

Example 2— Injectability, Cytocompatibility and Cellular Infiltration ofTropoelastin In vivo studies were conducted to assess the injectability,cytocompatibility and stability of the tropoelastin-PNPHO hydrogels usedin accordance with the instant invention. The high tissue adhesiveproperties and fast gelation time of the tropoelastin-PNPHO eradicatedthe need for sutures or any other physical supports to constrain theinjected hydrogel in place. The hydrogels were retained at the injectionsite for up to 8 weeks (FIG. 2 ). The explanted samples were used tohistochemically assess the cytocompatibility and in vivo biologicalproperties of the implants at different time points.

Results from haematoxylin and eosin (H&E) stained samples showedoutstanding cytocompatible properties of the tropoelastin hydrogels.Only a mild inflammatory response to tropoelastin was observed one weekinjection. The H&E staining of samples, as shown in FIG. 3 demonstratedthat the fibrous tissues around the hydrogel had settled in the periodone week to two weeks post-surgery. Milligan's trichrome (MT) stainingof the week two samples in FIG. 3 shows dermal fibroblast infiltrationand de novo collagen deposition within the tropoelastin hydrogels.

Example 3— Sheep Model of Bone Repair

The ovine model was accomplished as an osteotomy from Anterior toPosterior surfaces through the tibial shaft. All sheep were 2 to 3 yearsof age. Following anaesthesia, an oscillating bone saw was used toresect a 3 mm segment of the right mid diaphyseal tibia of each sheep(FIG. 4A). The injured bone site was stabilised with a standard 13 mmlong, 3.5 mm bone plate and 2.5 mm offset secured to the non-drilledaspect of the tibial corticalis by appropriate screws (FIG. 4 ). Thebone gap was then filled with tropoelastin containing hydrogels or leftempty as the negative control. The tropoelastin-containing hydrogelswere either a PNPHO-based hydrogel (TE-PNPHO hydrogel) (FIG. 4B) or aHA-based hydrogel (TE-HA hydrogel) (FIG. 4C). Tropoelastin-containinggels were readily injected into the osteotomy site, where theycompletely filled the gap. The surgical wound was closed with 3/0polydioxanone subcutaneous and intradermal continuous sutures.

X-ray computed tomography (CT) scans were conducted at 0, 4 and 8 weekspost-surgery. The specimen were harvested at 8 weeks post-surgery forhistological analyses.

Results

A. Controls

Selection of the specimen was difficult as the bone fell apart whenattempting harvesting of the osteotomy.

Microscopic features observed: periosteum was mildly thickened byhyperplastic cells with minimal amounts of intercellular collagenousmatrix (FIG. 5 ) The defect in the bone was filled with immature wovenbone with inter trabecular spaces that were filled with undifferentiatedvascular tissue. Mild remodelling of the seams of the osseous trabeculaewas present as a sprinkling of osteoclastic resorption sites and plumposteoblasts lining some of the osseous seams.

Immature woven bone was formed and was denser at the periosteal surfacesas compared with the endosteum region. Bone marrow tissue were presentat the endosteum region. The strength of the bone without the mechanicalplate was minimal.

B. Test samples:

Selection of samples was relatively easy as the osteotomy and bone heldtogether as samples were collected/harvested.

Microscopic features observed (FIG. 5 ): an open well of approximately 5mm covered by a periosteal layer mostly of fibrous tissue contained afew small osseous trabeculae. The walls of the well were mainly composedof the corticalis from the shaft of the tibia (prior to sawing). Somerecently formed bone occurred in the apparent deep corners of the wellbut most of the well contained open moderately dense fibrovasculartissue with occasional small osseous trabeculae. The floor of the wellwas approximately 3 mm in thickness of dense reparative compact bone.This arch shaped dense bone appeared to be endosteal derived.

Strong cortical bone was formed at the endosteum region. The formationof cortical bone at the endosteum allows fast recovery of the mechanicalstrength of the tissue. Some trabecular bone was also observed at theosteotomy site, close to the periosteum. The osteotomy hap was decreasedfrom 3 mm to 1.8 mm. Endosteal compact cortical bone joined the tibialdiaphyseal segments. Considerable strength had been achieved by theendosteal reparative bone.

CT images of osteotomy sites (FIG. 6 ) were taken at 0, 4 and 8 weekspost-surgery and show sharp cut lines across the bone immediately aftersurgery which begin to blur by 4 weeks and fill-in by 8 weeks as thebone repairs. Treatment of the bone defect with tropoelastin-containinggels appeared to both accelerate and enhance bone healing suggestingthat the materials are both osteoconductive and osteoinductive.

DISCUSSION

The controls defects were filled with open trabecular bone that occupiedthe osteotomy to the periosteal fibrous layer and could be tracedextending from the marrow tissue. The strength of the bone without themechanical plate was minimal.

In contrast the test specimens had formed a dense arch of endostealcompact bone joining the tibial diaphyseal segments.

Although much of the osteotomy had not filled with osteogenic tissueconsiderable strength had been achieved by the endosteal reparativebone. Such allowed the specimen to be harvested without breaking afterremoval of the mechanical plate and screws.

Example 4— Rabbit Model of Bone Defect Repair

Experimental Design

Animals: New Zealand white rabbits, 7-8 months old, 3.0-4.5 kg.N=6/group.

Groups 1 and 2:

Critical-sized bone defects were made to the medial femoral condyle ofanimals. Defects were 3 mm diameter, 3 mm depth (full thickness) (FIG.7A). Defects were injected with cylindrical grafts containingtropoelastin (group 1, test animals) or carrier (group 2, controlanimals).

Repairs of the defects were assessed at 4 and 8 weeks following injuryand injection of the grafts.

Analysis:

Repair of the defects were assessed using imaging techniques (pCT andMRI) and histological analysis (Hematoxylin and eosin to determinenormal histological features, Masson's trichome (to assess collagenfibers) and immunohistochemistry (to detect tropoelastin).

Results:

The tropoelastin gel retained at the injection site (FIG. 7 ). Also, theinjection of tropoelastin gel at the site of injury in rabbits resultedin formation of bone. μCT analysis showed an increase in bone volume atweeks 4 and 8 for test animals compared to control animals (FIG. 8 ).The results from the μCT analysis showed that injection of tropoelastingel in critical sized bone defects significantly enhanced the tissueregeneration in compared with control groups (empty voids).

Example 5: Synthesis of TE-HA Hydrogels

Hydrogels comprising tropoelastin with hyaluronic acid as a scaffold(TE-HA hydrogels) were made by combining a solution of recombinant humantropoelastin (200 mg/ml) with phosphate buffered saline followed by theaddition of derivatised HA, to a final concentration of approximately 50mg/ml. The combination was mixed thoroughly followed by briefcentrifugation to remove air bubbles. The material was left for 30 minat room temperature to formulate. The hydrogel was then filled into asterile 1 ml syringe in a laminar flow hood.

Similar hydrogels were made in this way, comprising tropoelastin at afinal concentration of about 10 mg/ml to 100 mg/ml.

The formulations made in this way all presented with the properties offirm materials which were extrudable through fine gauge 27G needles ascoherent threads of 10-20 cm in length.

The tropoelastin hydrogels made in this way contained high levels ofnon-cross-linked tropoelastin such that the tropoelastin was free to bereleased from the hydrogel at the site of delivery and to be able to actto promote bone formation.

Tropoelastin hyaluronic acid hydrogels made in this way were utilised invarious in vivo experiments and showed increased persistence time, andability to induce bone formation (as shown in Example 3).

Example 6: Synthesis of TE-PNPHO Hydrogels

Hydrogels comprising tropoelastin with PNPHO as a scaffold (TE-PNPHOhydrogels) were made by combining tropoelastin and PNPHO to a finalconcentration of 30 mg/ml tropoelastin and 10 mg/ml PNPHO (equivalent toa 1:1 molar ratio).

In one method PNPHO copolymer was dissolved in PBS for 24 hr.Tropoelastin solution was added to PNPHO solution and incubated at 4° C.for another 24 hr.

In an alternative, dissolution of PNPHO and protein conjugation wereconducted at the same time.

In a third method PNPHO was dissolved and conjugated with naturallyderived protein on a shaker.

In a further method PNPHO-tropoelastin conjugate powder was formed byfreeze drying PNPHO-tropoelastin solution. The conjugate powder wasdissolved in PBS on a shaker to form the final polymeric solution.

The tropoelastin-PNPHO solutions formed with different techniques wereconverted to hydrogels by increasing the temperature to 37° C. Thetropoelastin hydrogels made in this way contained high levels ofnon-cross-linked tropoelastin such that the tropoelastin was free to bereleased from the hydrogel at the site of delivery and to be able to actto promote bone formation. These hydrogels were utilised in various invivo experiments and showed increased persistence time, and ability toinduce bone formation (as shown in Examples 1-4).

SEQ ID NO: 1 SHEL526A amino acid sequence:Gly Gly Val Pro Gly Ala lle Pro Gly Gly Val Pro Gly Gly Val Phe Tyr ProGly Ala Gly Leu Gly Ala Leu Gly Gly Gly Ala Leu Gly Pro Gly Gly Lys ProLeu Lys Pro Val Pro Gly Gly Leu Ala Gly Ala Gly Leu Gly Ala Gly Leu GlyAla Phe Pro Ala Val Thr Phe Pro Gly Ala Leu Val Pro Gly Gly Val Ala AspAla Ala Ala Ala Tyr Lys Ala Ala Lys Ala Gly Ala Gly Leu Gly Gly Val ProGly Val Gly Gly Leu Gly Val Ser Ala Gly Ala Val Val Pro Gln Pro Gly AlaGly Val Lys Pro Gly Lys Val Pro Gly Val Gly Leu Pro Gly Val Tyr Pro GlyGly Val Leu Pro Gly Ala Arg Phe Pro Gly Val Gly Val Leu Pro Gly Val ProThr Gly Ala Gly Val Lys Pro Lys Ala Pro Gly Val Gly Gly Ala Phe Ala GlyIle Pro Gly Val Gly Pro Phe Gly Gly Pro GIn Pro Gly Val Pro Leu Gly TyrPro Ile Lys Ala Pro Lys Leu Pro Gly Gly Tyr Gly Leu Pro Tyr Thr Thr GlyLys Leu Pro Tyr Gly Tyr Gly Pro Gly Gly Val Ala Gly Ala Ala Gly Lys AlaGly Tyr Pro Thr Gly Thr Gly Val Gly Pro Gin Ala Ala Ala Ala Ala Ala AlaLys Ala Ala Ala Lys Phe Gly Ala Gly Ala Ala Gly Val Leu Pro Gly Val GlyGly Ala Gly Val Pro Gly Val Pro Gly Ala Ile Pro Gly Ile Gly Gly Ile AlaGly Val Gly Thr Pro Ala Ala Ala Ala Ala Ala Ala Ala Ala Ala Lys Ala AlaLys Tyr Gly Ala Ala Ala Gly Leu Val Pro Gly Gly Pro Gly Phe Gly Pro GlyVal Val Gly Val Pro Gly Ala Gly Val Pro Gly Val Gly Val Pro Gly Ala GlyIle Pro Val Val Pro Gly Ala Gly Ile Pro Gly Ala Ala Val Pro Gly Val ValSer Pro Glu Ala Ala Ala Lys Ala Ala Ala Lys Ala Ala Lys Tyr Gly Ala ArgPro Gly Val Gly Val Gly Gly Ile Pro Thr Tyr Gly Val Gly Ala Gly Gly PhePro Gly Phe Gly Val Gly Val Gly Gly Ile Pro Gly Val Ala Gly Val Pro SerVal Gly Gly Val Pro Gly Val Gly Gly Val Pro Gly Val Gly Ile Ser Pro GluAla GIn Ala Ala Ala Ala Ala Lys Ala Ala Lys Tyr Gly Val Gly Thr Pro AlaAla Ala Ala Ala Lys Ala Ala Ala Lys Ala Ala GIn Phe Gly Leu Val Pro GlyVal Gly Val Ala Pro Gly Val Gly Val Ala Pro Gly Val Gly Val Ala Pro GlyVal Gly Leu Ala Pro Gly Val Gly Val Ala Pro Gly Val Gly Val Ala Pro GlyVal Gly Val Ala Pro Gly Ile Gly Pro Gly Gly Val Ala Ala Ala Ala Lys SerAla Ala Lys Val Ala Ala Lys Ala GIn Leu Arg Ala Ala Ala Gly Leu Gly AlaGly Ile Pro Gly Leu Gly Val Gly Val Gly Val Pro Gly Leu Gly Val Gly AlaGly Val Pro Gly Leu Gly Val Gly Ala Gly Val Pro Gly Phe Gly Ala Val ProGly Ala Leu Ala Ala Ala Lys Ala Ala Lys Tyr Gly Ala Ala Val Pro Gly ValLeu Gly Gly Leu Gly Ala Leu Gly Gly Val Gly Ile Pro Gly Gly Val Val GlyAla Gly Pro Ala Ala Ala Ala Ala Ala Ala Lys Ala Ala Ala Lys Ala Ala GInPhe Gly Leu Val Gly Ala Ala Gly Leu Gly Gly Leu Gly Val Gly Gly Leu GlyVal Pro Gly Val Gly Gly Leu Gly Gly Ile Pro Pro Ala Ala Ala Ala Lys AlaAla Lys Tyr Gly Ala Ala Gly Leu Gly Gly Val Leu Gly Gly Ala Gly Gin PhePro Leu Gly Gly Val Ala Ala Arg Pro Gly Phe Gly Leu Ser Pro Ile Phe ProGly Gly Ala Cys Leu Gly Lys Ala Cys Gly Arg Lys Arg Lys

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1. A method of inducing formation of bone in an individual including thestep of providing an individual requiring bone formation, providing atherapeutically effective amount of tropoelastin to the individual toinduce the formation of bone in the individual, thereby inducing boneformation in the individual.
 2. The method of claim 1 wherein theindividual has a bone defect in which bone formation is required.
 3. Themethod of claims 1 or 2 wherein the defect is a fracture or void.
 4. Themethod of claim 3 wherein the defect is a fracture and the individual isprovided with tropoelastin to promote the repair of the fracture.
 5. Themethod of claim 4 wherein the tropoelastin is administered directly tobone at the site of the fracture.
 6. The method of any one of thepreceding claims wherein the tropoelastin is administered directly tothe bone callus.
 7. The method of any one of the preceding claimswherein the tropoelastin is administered by injection.
 8. The method ofclaim 6 wherein the tropoelastin is administered in the form of a gel,putty or paste.
 9. The method of claim 8 wherein the tropoelastin isadministered to a periosteal surface.
 10. The method of claim 3 whereinthe defect is a void.
 11. The method of claim 10 wherein thetropoelastin is administered directly to bone at the site of the bonevoid.
 12. The method of claim 11 wherein the tropoelastin isadministered directly to the bone callus.
 13. The method of claim 12wherein the tropoelastin is administered by injection.
 14. The method ofclaim 13 wherein the tropoelastin is administered in the form of a gel,putty or paste.
 15. The method of claim 14 wherein the tropoelastin isadministered to a periosteal surface.
 16. The method of claim 2 whereinthe bone defect is low bone density.
 17. The method of claim 16 whereinthe tropoelastin is administered to a periosteal surface.
 18. The methodof claim 16 wherein the tropoelastin is administered to an endosteumregion.
 19. The method of claim 18 wherein the tropoelastin isadministered to an endosteum region by micro-drilling of cortical bone.20. A method of any one of the preceding claims wherein the tropoelastinis SHELδ26A, as shown in SEQ ID NO: 1.